Every time we eat fried food, we also ingest some of the frying oil – for instance 6 % with chips and 14 % with fried turnovers.

To ensure that the fried foods are easy to digest and taste great, the frying medium and the food itself must be of premium quality. It has to be in optimum condition – in accordance with both, food safety legislation and a sensory perspective. The A – Z of Oil Quality provides helpful insights.

Frying Oil Quality

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Seven enemies are ready to attack! This may sound dramatic. Well, it is.

Heat fosters the degradation of oil. Prior to, during and after frying, other factors and handling errors can accelerate the decline of the oil quality.

  1. Oil temperature too high or too low
  2. Cleaning product and soap residue
  3. Water in all aggregate states
  4. Salt and seasonings
  5. Food residue and carbon
  6. Light – UV radiation
  7. Air – oxidation

These seven factors are definitive culprits when it comes to frying oil or fat. If you devise the proper strategy, you can manage them.

Frying Oil Quality

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They may be chemical or physical – a slew of things happen while frying that can spoil the quality of the fat.

The process of frying is complex. The positive Maillard reaction (which gives the fried food its golden brown color) is accompanied by various unwanted heat effects. This includes e.g. the generation of polymerized triglycerides and polar compounds, the Total Polar Materials (TPM). These TPM are the factors used to determine whether frying oil quality is good or bad.

Maillard reaction

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From the A – Z: B as in Beer

Measuring technology is required to determine the percentage of polar compounds in the oil. With a measuring tolerance of +/- 3 % this is a safe and precise method. However, what can be done if such tools are not available?

If your fryer produces a fine head of foam like a fresh pint of beer from the tap, you have to change your oil right away.

The progression of the decline in quality of the grease in frying oil becomes visual when this fine foam appears on the surface. The finer and denser it is, the lower the quality of the used oil. Transparent white large bubbles in the hot oil, on the other hand, confirm that the oil is fresh.


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frying oils and frying fats

From the A – Z: C as in Color

Your frying oil may be dark brown and you arrive at the conclusion that it’s high time to change the oil. However, if you measure the polar compound content, the oil may still be in the optimum range of 14–18 % TPM.

What appears to be a contradiction is actually quite common in everyday practical situations because the color of frying oils and fats is not a quality criterion. What counts is the polar compound = TPM percentage, as it determines the quality level of frying oil.

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More Tips and Tricks for Better Quality Oil
  1. Never heat up the oil to temperatures above 170 °C. Higher temperatures will neither make the fried foods crispier nor speed up the cooking time. All higher temperatures do is increase the degradation of the fat.
  2. Never add food items to be fried straight from above the fryer. Crumbs and ice crystals will drop directly into the oil and accelerate the decline of the oil quality.
  3. The maximum ratio of food to be fried and fryer filling level should be 1:10. Failure to comply with this rule will result in an extreme drop of the frying temperature and the frying food will absorb a lot of oil.
  1. If there are extended breaks between frying cycles, do not allow the temperature of the oil to drop below 120 -130 °C as hydroperoxides will develop below this temperature range.
  2. Use oil consisting of the optimal combination of monosaturated (temperature stability) and polysaturated (typical fried food flavor) fatty acids.
  3. Visually, you will be able to determine the quality of the oil based on the foam development. Transparent large bubbles are good, while a foamy appearance tends to be more critical.
  4. The color of the oil is not a quality criterion.
  5. Food will not begin to absorb unwanted oil until you have removed the fried food from the fryer. Make sure you allow it to drain well and quickly.

Frying Oil Quality